This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1899 Excerpt: ...doubtless occurs in small individuals in some specimens. Somewhat rarely the pyritic accessory has the golden-yellow color of chalcopyrite. The garnet and quartz are not contact minerals, as Teall seems to regard them,1 but rather accessories and alteration products, to be found wherever alteration appears, whether ...
Read More
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1899 Excerpt: ...doubtless occurs in small individuals in some specimens. Somewhat rarely the pyritic accessory has the golden-yellow color of chalcopyrite. The garnet and quartz are not contact minerals, as Teall seems to regard them,1 but rather accessories and alteration products, to be found wherever alteration appears, whether brought about by weathering or by the deeper-seated change of metamorphism. The garnets are undoubtedly present in all contact alterations also, and perhaps have a still wider distribution than either weathering or deeper-seated alteration alone would produce. The quartz is regarded as partly an infiltration product and partly a by-product of the alteration of the augite to hornblende or biotite, or, as is often the case, to both. Among the minerals which may be regarded as purely resultant products of decomposition, hornblende should certainly occupy the first place. Yet it is not safe to assume that all the hornblende is of this nature, for there is no sure means of determiDing the primary or the secondary origin of portions of this material. There is no doubt of the secondary development of by far the larger portion. It lies around the areas of pyroxene in such a manner as to preclude all doubt of its origin; it takes the place of pyroxene where such areas have become completely changed to a finely granular, bright-green, hornblendic segregation; and, finally, it shows a fibrous condition and a semigranular state within the feldspar areas, thus pointing to the breaking up of many individuals of this mineral. It may be said, in passing, that the parallel growth of augite and its resulting hornblende is very rarely seen; perhaps a half dozen sections were noted in the examination of these rocks which show this parallel position of host and produ...
Read Less
